The invention is directed to a method for the parameterization of a reception means of a radio system with allocated antenna means and with a pre-filter and to such a reception means or, respectively, a radio station with at least one reception means.
In a radio system, information is transmitted from a transmitting radio station to a receiving radio station. This information arrives at the receiving radio station in the form of reception signals. Due to various external influences, the reception signals reach the receiving radio station over a plurality of transmission paths. The signal components corresponding to the various transmission paths arrive at the receiving radio station at successive points in time. There is then the problem in the receiving radio station of equalizing these signal components, which can also be influences by further noise components, of correcting the errors and decoding the transmitted information.
Proakis,xe2x80x9cDigital Communicationsxe2x80x9d, 1989, pp.593-595 discloses pre-filters that suppress noise components in the reception signals, particularly adjacent channel interference, in a reception means before the detection. A pre-filer is composed of delay elements in which the reception signals are delayed in steps. The reception signals with different delay are respectively weighted with a filter coefficient and are subsequently summed up. The filter coefficients, however, are permanently prescribed, and the pre-filter is part of an equalizer, whereby the detector is fashioned as a simple threshold decision unit.
Further parameters are defined within the reception means for the evaluation of the reception signals. For example, these parameters are channel coefficients known from W. Koch,xe2x80x9cOptimum and sub-optimum detection of coded data disturbed by time-varying intersymbol interferencexe2x80x9d, IEEE Proceedings 1990, pp. 1679-84. These channel coefficients used in a channel model serve the purpose of suitably superposing various signal components of a reception signal that arrive after one another.
It is also known to supply the antenna data acquired from the reception signals by transmission into the base band and analog-to-digital conversion as well as the channel coefficients to a detector that equalizes the antenna data and undertakes the error correction. The symbols of the signals reconstructed in the output of the detector are subsequently decoded in a decoder, for example a Viterbi decoder.
It is known from mobile radiotelephone systems (see M. Mouly, M.-B. Pautet,xe2x80x9cThe GSM System for Mobile Communicationxe2x80x9d, 49. rue Louise Bruneau, F-91120 Palaiseau, France, 1992, pp. 231-237) to utilize what are referred to as training sequences in order to equalize receiving radio stations. At predetermined points in time, the transmitting radio station transmits a sequence of digital data that are known to the receiving radio station, i.e. whose data are present undistorted in the receiving radio station.
It is an object of the present invention to provide a method for the parameterization of a reception means as well as such a reception means or, respectively, radio station in a radio system that enable an adjustable and improved immunity to disturbance.
In a radio system, a reception means with pre-filter is parameterized in that the filter coefficients of the pre-filter are adjustable, and a matching of the pre-filter to a given demand for immunity to disturbance ensues adaptively during the operation of the reception means together with the determination of channel coefficients. It is thus possible to do justice to modified reception conditions. Such a parameterization of the reception means proves advantageous precisely in radio systems since the conditions in the radio channel change fast. For example, training sequences known in radio systems are suitable for setting the filter coefficients.
According to an advantageous development of this inventive method, received reception signals are converted into digital signals in the reception means and are delayed by steps in the adaptive pre-filter belonging to the reception means; the differently delayed reception signals are respectively weighted with filter coefficients and superposed. The reception means also contains a channel model with which the radio channel between transmitting and receiving radio station can be simulated. The channel model is thereby characterized by channel coefficients with which the channel model is matched to the real radio channel. The channel model represents, for example, a filter with finite pulse response. The antenna data and the specific channel coefficients are supplied to a detector for equalization and error correction of the antenna data that is contained in the reception means.
During a training sequence, the signals represent received test data that are additionally present undisturbed in the reception means. Antenna data allocatable to the received test data and model quantities derived from the channel model supplied with the test data are supplied to an arithmetic unit. The filter coefficients for the suppression of received noise quantities and the channel coefficients for the equalization of the differences in running time of various signal components of a reception signal are now simultaneously determined in the arithmetic unit, which likewise belongs to the reception means. To that end, an algorithm is utilized that undertakes the minimization of the deviation of antenna data of the training sequence and model quantities of the training sequence. The determined filter coefficients and channel coefficients can subsequently also be used for the evaluation of the signals outside the training sequence. When processing digital reception signals, it is possible to realize pre-filter, channel model and arithmetic unit in a digital signal processor, additional circuit-oriented outlay being reduced as a result thereof.
The combination of adaptive pre-filter and channel model as well as the simultaneous calculation of the parameters for the filter coefficients and the channel coefficients in an arithmetic unit creates a significant improvement of the functioning of the reception means with respect to the reconstruction of transmitted information. The parameters required for setting the reception means can be determined in common with a simple algorithm. The secondary condition must thereby be noted that the trivial solution with filter coefficients and channel coefficients set to the value zero is precluded. A corresponding secondary condition is to be provided in the algorithm
Dependent on the plurality of delay elements of the adaptive pre-filter, an improved noise signal suppression ensues both for noise sources in adjacent channels as well as in the proper channel, particularly sine-shaped noise sources. The number of sine noise sources that can be completely eliminated corresponds to the number of filter coefficients minus one. The adaptive pre-filter produces a clear improvement of the reception quality, as a result whereof, given employment of the radio station in a radio system, a gain in system capacity also derives, for example in mobile radiotelephone systems due to the greater density of mobile stations thereby enabled.
According to further developments of the subject matter of the invention, the algorithm for determining the filter coefficients and channel coefficients is fashioned such, upon exclusion of the trivial solution, that a plurality of sets of filter coefficients are present in the reception means with which the received test data are respectively evaluated and, subsequently, the channel coefficients are determined with a minimum deviation from antenna data and model quantities. The solution with the least deviation, i.e. the appertaining filter coefficients and specific channel coefficients thereto, is selected and serves for the parameterization of the reception means. This solution reduces the calculating outlay to the determination of the channel coefficients, whereas the filter coefficients are selected from a set of known filter coefficients.
An alternative version is comprised in utilizing the calculation of the least error square or a correlation calculation for the determination of the filter coefficients and of the channel coefficients without pre-selection, and, accepting greater calculating outlay, thus selecting the filter coefficients and channel coefficients from an infinitely great set of possible values, but again upon exclusion of the trivial solution. The trivial solution wherein filter coefficients and channel coefficients are set to zero corresponds to a possible but senseless solution. Consequently, it is necessary to fix one of the filter coefficients or of the channel coefficients to a value unequal to zero.
According to another advantageous development of the invention, a synchronization of the received test data with the test data processed in the channel model is undertaken before the ultimate determination of the filter coefficients and channel coefficients. Due to an unforeseeable running time of the reception signals of the training sequence between transmitter and receiver, the point in time of the arrival of the received test data in the reception means cannot be predicted with absolute certainty. A delay with which the reception signals are charged in the reception means is therefore calculated in order to assure the beginning of the training sequence and an effective calculation of the filter coefficients without the disturbing influence of an inadequate synchronization. For example, the delay can be determined in that a minimization of the deviation is undertaken at a number of positions of the data stream of the antenna data and the optimum solutionxe2x80x94which corresponds to the synchronizationxe2x80x94is selected. Subsequently, this delay is also used outside of the training sequence.
The remaining patent claims recite a radio station whose reception means is appropriately fashioned for the implementation of the parameterization. Advantageously, this radio station is utilized in radio systems that are operated in time-slot multiplex and the parameterization is redetermined for each individual time-slot. An example of a radio system operated in time-slot multiplex are [sic] mobile radiotelephone systems (GSM, GSM-like) or cordless communication systems (DECT), whereby the radio station is operated as base station or mobile station. The inventive reception means or, respectively, radio station and the inventive method particularly do justice to the specific conditions of a mobile radiotelephone system since changing propagation conditions derive due to the mobility of communication terminal equipment, whereupon the parameterization of the reception means can be correspondingly adapted.